The invention relates to a viscosity-type torsional vibration damper and to a method of manufacturing a viscosity-type torsional vibration damper.
Viscosity-type torsional vibration dampers in the many different embodiments have been known for a long time. The viscosity-type torsional vibration damper is a machine element which is preferably mounted at the crankshaft end of internal-combustion engines for the purpose of limiting torsional strains which result from the oscillating gas forces and inertial forces in the crankshaft.
The mass moment of inertia of the seismic ring, the gap geometry as well as the viscosity of the damping medium are relevant for the operation of the torsional vibration damper. The housing has the task of guiding the seismic ring over bearing surfaces and receiving the damping medium.
Since the housing is rigidly connected with the crankshaft, it causes, as the result of its mass, a lowering of the sympathetic vibration frequency of the mass system.
This may have the result that sympathetic vibrations of lower ordinal numbers reach the operational rotational speed range. In principle, a housing which is as light as possible is advantageous for the vibration system; especially since the housing part to be damped is included in the available damper performance.
Corresponding to the state of the art, metallic materials, preferably steel or cast iron, are used as the material for the housing. Attempts to use inelastic plastic materials were not successful and, after a short time, were not continued (see the type-forming German Patent Document DE OS 21 30089).
Because of the increased power of internal-combustion engines and for acoustic reasons, elements for limiting the torsional strain of the crankshaft are increasingly also used in the utility vehicle and passenger car field. For cost reasons, rubber dampers had predominantly been used in this performance class although the viscosity-type torsional vibration damper is more efficient. So far, the construction principle of the viscosity-type damper has required more components and higher mounting expenditures in comparison to the rubber damper.
The invention aims at providing a viscosity-type torsional vibration damper which can be used and produced at reasonable cost also in the case of lower-powered engines.
The invention achieves this goal.
In contrast to the state of the art, the invention suggests the use of thermoplastic materials. Previously the use of these plastic materials was obviously not considered possible because of the opinion that a plastic material does not meet the requirements concerning the strength, the thermal transmission and the resistance to heat as well as the chemical stability with respect to the damping medium. Furthermore, no suitable economical manufacturing methods were known. The invention refutes this prejudice. It also reduces The number of components and the manufacturing expenditures.
When a thermoplastic glidable plastic housing is used, no additional bearing elements are required for guiding the rotating ring. Furthermore, the machining expenditures for the components will be reduced because no cutting machining is required. The lower density of the plastic material results in a considerable reduction of weight. With respect to the acoustic behavior, a plastic housing exhibits better damping characteristics than a metallic housing.
In addition to the one-piece variant, it is particularly advantageous to construct the viscosity-type torsional vibration damper as two or more parts.
In the following, the invention will be explained in detail by means of embodiments with reference to the drawing.